The object of the present invention is a continuous-working gas-blast pipe, partially immersed in a metallurgical melt, for feeding reaction agents into the metallurgical melt. The gas-blast pipe has in the center a reaction-agent pipe, which is surrounded by cooling-medium pipes, parallel to it and having a smaller diameter than the reaction-agent pipe. In addition, the cooling-medium pipes and the reaction-agent pipe are lined with a ceramic material.
Thus, the invention relates to a device by means of which reaction agents, e.g. oxygen-bearing of other reaction gases, are fed into metallurgical melts formed by smelting processes known per se. By means of these reaction agents, the impure products of smelting, for example a sulfur- and/or carbon-bearing one, are converted in the same smelting unit into the final product of conversion processes known per se.
Methods disclosed in various patents are discussed below in order to illustrate the state of the art of devices intended for feeding reaction agents into metallurgical melts.
For feeding reaction agents into metallurgical melts there is, for example, a liquid-cooled oxygen-blast pipe known from U.S. Pat. No. 3,751,019. In liquid cooling, fracturing of the coolant pipe causes the coolant to pass into the melt, a factor which is a work safety hazard owing to the drastic reactions produced. Furthermore, in the said oxygen-blast pipe there is no separate nozzle part at the end of the reaction-agent pipe, and so the velocity of the reaction agent in the blast is low and the penetration of the reaction agent into the metallurgical melt is therefore poor. In addition, the reaction agent is blown vertically in the said oxygen-blast pipe, a factor which sets additional requirements of the material used for lining the floor of the smelting unit.
U.S. Pat. No. 3,843,105 discloses a liquid-cooled, non-continuous-working oxygen-blast pipe. The oxygen-blast pipe is surrounded by cooling-agent pipes, in which the coolant is, for example, water. In addition, at the lower end of the oxygen-blast pipe there are cooling flanges made from copper and coated with a refractory material. Various patents also disclose non-continuous-working devices for blowing gaseous and/or solid reaction agents into metallurgical melts. These devices utilize the cooling effect of liquid cooling methods (FI Pat. No. 40,236, DD Pat. No. 122,313), of reaction slag (DE Pat. No. 2,819,587) and of the blown gas (DE Pat. No. 2,117,714). It must, however, be taken into consideration that these non-continuous-working gas-blast pipes are primarily intended for the conversion methods of the steel industry, in which case the uninterrupted blowing time and possible partial immersion in the melt is only 30-40 min. Therefore, the cooling methods used in them cannot be directly applied to continuous-working gas-blast pipes.
From U.S. Pat. No. 3,529,955 there is known a gas-blast pipe which is installed partly immersed in the melt and in an oblique position in relation to the melt. The gas-blast pipe is cooled by directing a cooling liquid into the reaction-agent pipe situated in the center of the gas-blast pipe; dispersed into small drops and at the same time vaporizing, the cooling liquid passes into the metallurgical melt together with the reaction gas. In this case, the velocity of the gas must be low in order that all the cooling-liquid drops have time to vaporize. On the other hand, a low velocity of the gas has an adverse effect on the penetration of the reaction agent into the metallurgical melt.
Furthermore, U.S. Pat. No. 3,758,090 discloses a blast pipe which is suitable for blowing fuel and oxidizing gas via a tuyere in the wall of the smelting unit. By means of burners, the liquid fuel is caused to burn with oxygen or oxygen-enriched air in the blast pipe. The gas mixture is fed into the smelting unit as a turbulent gas flow through a Laval nozzle known per se, whereby the gas flow velocity increases to a value of 300-500 ms.sup.-1. Since the blowing takes place through a tuyere, the wall of the smelting unit alone provides sufficient cooling for the blast pipe. Therefore, an actual cooling system need not be constructed for the blast pipe. However, the cooling effect of the tuyere is so great that it at the same time causes a decrease in the melt temperature. Thereby, for example, solidified slag deposits are produced at the mouth of the tuyere, and these deposits clog the tuyere. Furthermore, in order for the tuyere blast to be as effective as a gas-blast pipe partially immersed in the metallurgical melt, tuyeres should be constructed in different parts of the smelting-unit wall, and this would have an adverse effect on the control of the smelting process.
The object of the present invention is to eliminate the disadvantages of the gas-blast pipes described in the above-mentioned patents.